The Responsorial verse is: "The Lord will guard us as a shepherd guards his flock" (see Jeremiah 31:10-13).
Ezekiel 37:21-28 is God's solemn promise to restore unity among his People: "I will save them from all the apostasies into which they have fallen... They shall be my people."
But unity in doctrine requires unity in government. Some person or body must have the authority to determine what teaching is true and what is false. "My servant David shall be king over them; and they shall all have one shepherd." As the promised "Son of David," it is Jesus who exercises this role forever in his Church. But for his direction to be real and practical, not just matter for speculation, he must exercise his government through some identifiable and authoritative ruler or ruling body on earth. Otherwise people will argue forever about what Jesus really meant or desires. And quite often the arguments will be resolved by division into separate camps or churches. The promise, "I will make them one" requires the promise, "they shall all have one shepherd."
True discipleship in the Church is inseparable from unity with the Church. This unity is the sign of God's presence: "My dwelling place shall be with them; and . they shall be my people. Then the nations shall know that I the LORD sanctify Israel.." Jesus said the same of his Church: "I ask that they may all be one. As you, Father, are in me and I am in you. so that the world may believe that you have sent me" (John 17:21).
Luke 11:45-57 tells us how Jesus brings about this unity: "Jesus was about to die for the nation... to gather into one the dispersed children of God." We are kept united, not just by human obedience to divinely established human authority, but by the mystery of Christ's indwelling presence and action in the Church.
The mystery of Christ's death on the cross is that when Jesus died, we died in him. The mystery of Baptism is that we were "baptized into his death." We were incorporated into his body on the cross, died in him and rose again in him to live as his risen body on earth (Romans 6: 3-4, 6:8; 1Corinthians 15:18; 2Corinthians 5:14; Ephesians 2:6; Colossians 2: 12, 20, 3: 1-3; 2Timothy 2:11). Our unity is the unity of one living body, maintained by the real presence of Jesus living, acting, teaching and governing through the members of his body, the Church. Jesus is the Shepherd in the shepherds. As disciples of the Church, we are his disciples. As his disciples we must be disciples of the Church. Then "the Lord will guard us as a shepherd guards his flock."
Initiative: Be a disciple of the Church. Read the documents of Vatican Council II.